In the prior art, the ways for controlling the power saving of the operation of a motor includes by using capacitors, voltage reduction, and power control.
The way of using capacitor is to add capacitors before a motor for reducing virtual power and reduce current so as to save power consumption in wires. However, this way has the following disadvantages that the real power does not reduce and the power reduction in wires is farther smaller than the total power consumed by the whole circuit. This way is mainly used to high voltage or low load condition. However, this way cannot achieve the object of easy adjustment so as to harm the motor. An important feature of an AC motor is that the power consumption in a low load is smaller than the power consumption. The lower the load, the larger the power consumed. Thus a part of power can be saved. Using a silicon controlled semiconductor to control the power supply of a motor can reduce the power waste. This idea is firstly disclosed by Nola, 1977 in NASA, U.S. However, this can not resolve the current complicated motor operation conditions and power supply networks. Moreover, there are demands for the functions of full voltage or smooth start, power saving constant speed operation and full voltage or smooth stop; stopping operation in over current or over voltage, full voltage output in low voltage under in non-power saving mode; stopping operation of the motor under the state of losing phase in power or motor as the motor is in operation, but the prior art can not achieve all above mentioned functions.